The present invention relates to a forced induction apparatus for an engine including forced induction devices arranged next to each other in the vertical direction.
Japanese Laid-Open Patent Publication No. 2012-140890 describes an example of a known forced induction apparatus for an engine including multiple forced induction devices such as a multistage forced induction apparatus. There are various ways to lay out the forced induction devices. However, the forced induction devices are usually laid out in the vertical direction to reduce the occupied area.
The forced induction devices each include a shaft and bearings. The bearings, which rotationally support the shaft, are supplied with oil for lubrication and cooling. The oil supplied to the bearings is returned to an oil pan through a drain pipe, which is arranged below the forced induction device, and supplied again from the oil pan to the forced induction device by a pump. This forms an oil circulation passage.
When the forced induction devices are arranged next to each other in the vertical direction as described above, the space is narrow between the upper forced induction device and the lower forced induction device. Thus, the shape, size, layout, and the like of the drain pipe located below the upper forced induction device are limited. This may hinder smooth discharging of oil from the upper forced induction device and lower the oil discharging efficiency. When the space is widened between the upper forced induction device and the lower forced induction device to arrange the drain pipe below the upper forced induction device in a suitable manner, the volume occupied by the forced induction apparatus increases. This adversely affects the mountability of the forced induction apparatus.